A simple and scalable fabrication of a high-performance flexible microsupercapacitor using hierarchical Ni–Mo–S nanostructures decorated on Ti₃C₂T_x MXene

Abstract

The demand for improved energy storage technologies has increased globally in the new era of additional technological expectations. Energy storage performance can be improved by designing electrodes with hybrid architectures. For miniature and compact electronics, micro-supercapacitors (MSCs) with exceptional electrochemical performance and flexibility are required. It has been proposed that transition metal sulfides are a viable material with exceptional electrochemical performance for effective energy storage. Ionic electron mobility is sluggish, and working stability is low in single-component metal sulfides. For high-density hybrid interfaces, it is still difficult to develop well-defined hybrid metal sulfides with high 2D functional surfaces. This article reports on the in situ synthesis of a hybrid of Ni–Mo–S and MXenes, which has several applications in electrochemical energy storage. In this work, a one-step hydrothermal technique was employed for a hybrid structure on ultrathin Ti₃C₂T_x MXenes with Ni–Mo–S nanosheets. To develop solid-state flexible MSC on a micropatterned laser-scribed graphene (LSG), this work makes use of the potential of the Ni–Mo–S/Ti₃C₂T_x MXene hybrid structure as an electrode material. The ultrathin design, planar geometry of the interdigitated microelectrodes, and excellent conductivity and wettability work together to function as the current collector, allowing the Ni–Mo–S/Ti₃C₂T_x MXene hybrid structure to interact efficiently. At a current density of 5 mA cm⁻², the LSG-NMS/TCX MSC device exhibits an exceptional areal capacitance of 208 mF cm⁻². Furthermore, the LSG-NMS/TCX MSC device maintained an exceptionally high rate capability of 94.6% even after 10 000 charge–discharge cycles, achieving an outstanding energy density of 65.10 µWh cm⁻² at a power density of 4212 µW cm⁻². The fabricated LSG-NMS/TCX MSC displays mechanical flexibility that remains unchanged when subjected to various twisting and bending angles.

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1 Introduction

Energy storage has emerged as a primary challenge that can potentially be addressed by a variety of scientific and technical abilities to address current global energy and environmental challenges.^1,2 This is particularly relevant when it comes to investigating energy storage devices. Given its high-power density, quick charging and discharging, strong cycle stability, compact size and weight, and other characteristics, the energy storage technologies of the supercapacitor can offer exceptional opportunities for the effective conversion and storage of energy.^3,4

In electrically powered devices, electrochemical microsupercapacitors (MSCs) are being developed as a potential replacement for on-chip micropower units.^5,6 The advancement of microelectrochemical energy storage systems with minimized volume, basic modulation, durable adaptability, high energy density, and power densities has been substantially accelerated by the rapid improvements in wearable devices. Specifically, in-plane micro-supercapacitors (MSCs) have drawn a lot of interest owing to their miniature size, compact design, portability, high-power density, prolonged cycle life, and quick charge/discharge cycles.^7,8 In electrically powered devices, electrochemical microsupercapacitors (MSCs) are being developed as a potential replacement for on-chip micropower units. Recently, laser-scribed graphene (LSG) has drawn interest as a potential electrode material for electrochemical MSCs because of its effective direct-write approach, which avoids tedious multiple-step operations and complex photolithography techniques.^5,9,10 As previously demonstrated, laser-induced graphene (LIG) has a noteworthy benefit in this aspect as a graphene-based material that may be made exclusively from cyclic polymers. Polyimide (PI) is frequently utilized as the reference material for laser scribing procedures to construct thin and flexible electrodes for applications employing microsupercapacitors (MSCs).^5,6 Laser-scribed graphene (LSG) has attracted a lot of attention in energy storage research, considering its enormous surface area, suitable thermal stability, and outstanding conductivity. It has been extensively investigated for microsupercapacitor (MSC) devices due to its exceptional characteristics. The MSCs with pure LSG 3D frameworks perform admirably in terms of capacitance in the area of electrochemistry.^10,11 Numerous pseudocapacitive materials, including conducting polymers,¹⁰ metal hydroxides,^6,10 transition-metal oxides,^12,13 and transition-metal sulfide,^14,15 have recently been reported to be hybridized with LSG to increase the capacitance and energy density of LSG-based MSCs.

Recently, there has been a lot of interest in 2D transition metal carbides and/or nitrides (MXene) as potential pseudocapacitance electrode materials for the energy storage group, owing to its high metallic conductivity, hydrophilicity,¹⁶ redox reactivity on titanium atoms and surface functional groups, and 2D nature. The development of high-rate functioning electrodes for MSC implementation is the result of these intriguing properties. However, due to its restacking challenges, MXene is not currently able to demonstrate its full capabilities in the development of MSCs. Therefore, one feasible approach is to find materials with robust electrochemical qualities that can improve their performance and lower MXene's tendency to stack.¹⁶ This approach seeks to maximize the overall performance of MXene-based MSCs to optimize them.

Recent studies and findings suggest that one of the key factors limiting the development of supercapacitors is the selection of an adequate and efficient electrode material. Given the narrow electron mobility path, superior electrical conductivity, and electrochemical reversibility, transition metal sulfides can enhance electrochemical performance by facilitating electron transport.¹⁷ Specifically for bimetallic sulfides, transition metal sulfides have demonstrated a distinct competitive benefit for the materials used for electrodes in supercapacitors, owing to their exceptionally high theoretical specific capacitance value. Owing to their distinct chemical attributes, plentiful abundance, accessibility, and ecological compatibility, the representative elements Ni and Mo have drawn a lot of interest in the field of transition metal-based materials for supercapacitor electrodes.¹⁶ In this perception, a lot of research has gone into producing Ni–Mo–S-based nanomaterials for use as supercapacitor electrodes. Compared to monometallic sulfides, bimetallic sulfides have richer active sites and redox reactions, as well as better conductivity.^11,18,19 The reversible redox behavior, affordability, and wide range of oxidation states of Ni–Mo-based chalcogenides make them promising candidates for application as supercapacitors. More precisely, Mo increases the electrical conductivity, whereas Ni-ions primarily disseminate high specific capacitance. A Ni–Mo–S-based device is anticipated to operate well as a supercapacitor, given the strong redox activity of Ni. Mo shows corrosion resistance and also increases the long-term endurance of the electrodes. Mo atoms also have several oxidation states spanning from +2 to +6. They demonstrate high electrical conductivity and higher capacity, making Mo-based bimetallic sulfides among these transition metal species with the highest research potential in energy storage.^20–22 Nevertheless, the capacity and stability requirements for supercapacitors are not feasible due to the inadequate conductivity and unavoidable agglomeration of Ni–Mo–S. Several key ideas, including morphological control, composite, and scaffold support strategy, have been attempted to address these shortcomings.²² Consequently, a hierarchical 2D nanoarchitecture with a few numbers of irregular defects could possibly be preferred in order to achieve optimum electrocatalytic performance of TM chalcogenides. Furthermore, distinctive surface dipoles have been reported to be generated through the efficient replacement of donor electrons in the 2D nanostructures. This may improve the chemical reactivity and stabilize metastable surface structures.^{16,17,22–24} Ni–Mo–S-based hybrid electrodes are therefore predicted to be the optimum electrodes for SCs because of their superior electrical conductivity and catalytic activity.

This article outlines the in situ synthesis of a hybrid of MXene and Ni–Mo–S, which has several uses in electrochemical energy storage. In this study, a hybrid structure on ultrathin Ti₃C₂ MXenes with Ni–Mo–S nanosheets was achieved using a one-step hydrothermal process. This study utilizes the potential of the Ni–Mo–S/Ti₃C₂T_x MXene hybrid structure as an electrode material to construct a flexible, solid-state MSC on micropatterned laser-scribed graphene (LSG). Together, the ultrathin design, planar shape of the interdigitated microelectrodes, and extraordinarily conducting superior wettability serve as the current collector that facilitates a smoother interaction between the Ni–Mo–S/Ti₃C₂T_x MXene hybrid structure. The NMS/TCX MSC device has an extraordinary areal capacitance of 208 mF cm⁻² at a current density of 5 mA cm⁻². Moreover, the LSG-NMS/TCX MSC device achieved an extraordinary energy density of 65.10 µWh cm⁻² at a power density of 4212 µW cm⁻², maintaining an extraordinarily high rate capability of 94.6% even after 10 000 charge–discharge cycles. Even when bent and twisted at different angles, the fabricated LSG-NMS/TCX MSC maintains its mechanical flexibility. The research findings indicate that LSG-NMS/TCX MSC has the potential to be used in flexible MSC applications in wearable and wireless microdevices in the future.

2 Materials and methods

2.1 Materials

For the synthesis of Ni–Mo–S and Ni–Mo–S/Ti₃C₂T_x MXene-based hybrid electrodes, a simple hydrothermal procedure is employed without further alteration. All analytical grade compounds were used for the synthesis. Ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O, SDFCL), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O, SDFCL), thioacetamide (C₂H₅NS, SRL), Red phosphorus (RP, ISOCHEM), ethylene diamine (C₂H₄(NH₂)₂, AVRA), K₂SO₄, ethanol LR (SDFCL), Nafion solution (5 wt% in a mixture of lower aliphatic alcohols and 45% water), hydrochloric acid (HCl), acetone LR, Ni-foam, Polyimide Kapton Tape, and distilled water.

2.2 Ti₃C₃T_x MXene etching

Al atoms from Ti₃AlC₂ (MAX-phase powder) were successfully etched using HF solution at room temperature to produce MXene (Ti₃C₂T_x).¹⁶ A Teflon-walled cylinder was first filled with 25 ml of 40% HF, and then 500 mg of coarsely ground Ti₃AlC₂ powder was gradually added to the mixture. After that, the mixture was subjected to intense magnetic stirring for 24 hours at room temperature. The resultant suspension was then repeatedly washed with distilled water until the pH reached a neutral level. The procedure was repeated. The powder was vacuum-dried for 12 hours and used further.

2.3 Synthesis of the Ni–Mo–S/Ti₃C₂T_x hybrid

Ni–Mo–S and the Ni–Mo–S/Ti₃C₂T_x hybrid are typically synthesized using 3 mM of Ni(NO₃)₂·6H₂O and 9 mM of (NH₄)₆Mo₇O₂₄·4H₂O after dissolution in 30 ml of distilled water. 12 mM of thioacetamide (C₂H₅NS) was progressively added. After that, the mixture was magnetically stirred for 45 minutes at room temperature in order to form a uniform solution. After that, the mixture was placed in a 50 ml Teflon-lined stainless-steel autoclave. The hydrothermal treatment was conducted at 200 °C for 12 hours. In order to grow the Ni–Mo–S/Ti₃C₃T_x hybrid, 30 mg of the obtained MXene powder was added to the precursors, and they were hydrothermally treated for 12 hours at 200 °C. After filtering, distilled water and ethanol were employed to clean the final product. The final step was to anneal the product in an Ar atmosphere for 3 hours at 350 °C after vacuum drying it for 12 hours at 60 °C. Fig. 1 depicts the stepwise synthesis process.

Fig. 1 A schematic of the composite formation: (upper panel) Ti₃C₂T_x MXene is synthesized from the Ti₃AlC₂ MAX phase, and NMS/TCX is synthesized using a straightforward hydrothermal process.

2.4 Material characterization

The phase identity and crystallographic features of the produced materials were examined using X-ray diffraction (XRD, Rigaku Ultima IV with Ni-filter for Cu-Kα radiation, λ = 0.1541 nm). An investigation of the elements, thickness of the substrate (cross-sections), and morphology was conducted using field emission scanning electron microscopy (FESEM, JEOL JSM-7100F, JEOL Ltd., Singapore). To examine the composition under an ultrahigh vacuum, X-ray photoelectron spectroscopy (XPS, Thermo K Alpha + spectrometer, Al Kα X-rays with 1486.6 eV energy) was used. Significant morphological and structural investigations were also conducted using transmission electron microscopy (TEM, TALOS F200S G2, 200 kV, FEG, CMOS camera 4k 4k).

2.5 Electrochemical characterization

The electrochemical performance of the materials NMS (Ni–Mo–S) and NMS/TCX (Ni–Mo–S/Ti₃C₂T_x MXene) was evaluated in 0.5 M K₂SO₄. Ag/AgCl and Pt wire served as the reference and counter electrodes, respectively, in a three-electrode setup used to study the redox process. Using a drop-cast method, electrodes were created on cleaned Ni foam (1 cm² area, 1 M HCl treatment, distilled water, and acetone LR). Then, 1 mg of electrode material was sonicated for 5–10 minutes in a 1 : 19 Nafion and ethanol solution. After being poured on the Ni-foam, a slurry was vacuum-dried at 60 °C. Following their pellet pressing in a hydraulic press at 5 tons of pressure, these electrodes were utilized as working electrodes. Electrochemical characterizations of the produced electrodes, including CV, GCD, and EIS, were performed via a CorrTest CS350 workstation in Wuhan, China. Using a sinusoidal potential of 5 mV and a frequency range of 0.01 Hz to 100 kHz, all electrodes were examined with EIS at the open circuit potential. The capacitance values and GCD profiles were used to determine the stability test.

2.6 Flexible all-solid-state microsupercapacitor fabrication

LSG patterning was done in accordance with previous reports.⁹ First, a PET film (0.1 mm thick) was masked over the PI tape. To engrave the programmed pattern, a CO₂ laser with a wavelength of 10.6 mm and a pulse duration of about 14 ms, an output power of 8.0 W, and a scan rate of 250 mm s⁻¹ was directed onto a PI tape masked with the PET film positioned horizontally. With a total working surface of 0.41 cm², LSG was patterned into 14 interdigitated electrodes (seven for each polarity), each measuring 5.67 mm in length, 0.35 mm in width, and 0.56 mm between the two adjacent electrodes. The interdigitated micro-pattern was left on the PI film after the PET sheet was fully removed. The NMS/TCX symmetric microsupercapacitor was fabricated by employing the spray coating technique. The NMS/TCX slurry was loaded using an airbrush technique for 10 seconds on masked LSG MSC arrays. The NMS/TCX LSG symmetric microsupercapacitor was vacuum-dried at 40 °C overnight, and the PET mask was then removed. The LSG-NMS/TCX microsupercapacitor device was encapsulated in a PVA-K₂SO₄ gel electrolyte. Fig. 6(a) illustrates the stepwise fabrication of a flexible all-solid-state LSG-NMS/TCX MSC device.

In order to formulate the PVA/K₂SO₄ gel, 1.7 g of PVA was progressively added to 25 ml of distilled water, and the mixture was continuously heated to 85 °C while being stirred until the solution turned clear. The solution mixture was gradually added to a 0.5 M K₂SO₄ solution until a consistent gel-like viscosity composition was achieved. The solution was kept at room temperature and then applied to the MSC for electrochemical analysis.

The areal capacitance values of LSG-MNS/TCX were calculated using the following equations, using CV and GCD profiles,²⁵

where A is the geometrical area of the electrodes, Δt is the discharge time, I is the current, and ΔV is the potential window. A (cm²) represents the entire area of the microelectrodes' active component. The 14 electrodes, comprising 7 positive and 7 negative constituents, are 5.67 mm in length and 0.5 mm in breadth. The MSC's two side arms measure 0.6 mm in width and 11.63 mm in length. Taking these measurements into account, the MSC's area is determined to be 0.41 cm².

The energy density (E) and power density (P) were calculated using the following equations,²⁵

where, C_a is a specific areal capacitance obtained from GCD, E is the energy density, ΔV is the potential window, and Δt is the discharging time.

3 Results and discussions

3.1 In Situ growth mechanism

The one-step hydrothermal synthesis procedure of MXene sheets and Ni–Mo–S nanoarchitectures from nickel nitrate hexahydrate, ammonium molybdate tetrahydrate, thioacetamide, and etched MXene powder precursors is shown in Fig. 1. The MXene etching procedure is shown in the inset panel. As described in the experimental “Ti₃C₂T_x MXene etching” Section (2.2), the Al layer was removed from the MAX phase using the extensively studied HF acid treatment. The consistent assembly of the positive metal source was made easier by the negatively charged surface functions (–O, –OH, and –F) on the MXene sheets following etching. These functional groups provide a surface that is highly electronegative and hydrophilic, enabling strong electrostatic and coordination interactions with Ni²⁺/Mo precursors, which lowers the nucleation energy barrier and allows for uniform nanosheet growth. The –O/–OH groups also provide effective anchoring sites for improved interfacial adhesion and reduced agglomeration of the MXene.^16,17 Thus, on the MXene sheets, a Ni–Mo–S nanosheet is formed. One of the primary functions of thioacetamide is as a sulfurizing agent. Moreover, as a regulated sulfur precursor, thioacetamide (TAA) is essential to the synthesis of nickel molybdenum sulfide (Ni–Mo–S). TAA breaks down gradually, releasing H₂S under hydrothermal or solvothermal conditions, resulting in a consistent supply of sulfide ions (S²⁻). The consistent formation of crystalline Ni–Mo–S phases, where Ni insertion improves the active edge sites and catalytic/electrochemical activity, becomes feasible by this regulated sulfurization, which also avoids uncontrolled precipitation.^25–29 Furthermore, the slow release of sulfide ions helps define the design of NiMoS nanostructures, such as nanosheets or architectures resembling flower petals, which increase the surface area and reveal more electroactive areas. As a result, TAA serves as a morphological regulator, performance enhancer, and sulfur donor in the formation of Ni–Mo–S nanosheets.

3.2 Material characterization

Fig. 2 displays the surface morphologies of Ni–Mo–S, abbreviated as NMS, and the Ni–Mo–S/Ti₃C₂T_x hybrid, abbreviated as NMS/TCX, which was synthesized using a single-step hydrothermal process. Fig. 2(a) displays the petal-like 2D thin nanosheets spread evenly to form a spherical structure resembling a flower-like morphology. Fig. 2(b) shows HF-etched MXene sheets. The layer separation shows that the Al layer was successfully etched from the MAX phase, and the impulsive etching process results in the overlapping, which creates a three-dimensional arrangement of MXene sheets, thereby providing an enlarged surface area.¹⁶ From Fig. 2(c and d), the as-synthesized Ni–Mo–S exhibits an extremely thin sheet-like structure. The super-thin 2D Ni–Mo–S nanosheets are evenly anchored on Ti₃C₂T_x nanosheets without permitting the unattached metal sulfide nanosheets to develop freely. This demonstrates that the metal precursor solutions were readily transformed into well-ordered, super-thin Ni–Mo–S nanosheets. The microstructures of the Ni–Mo–S/TCX sample at various magnifications show many nanosheets that are exquisitely and uniformly formed on the backbone of TCX MXene, as shown in Fig. 2(d). Ni–Mo–S nanosheets that resemble petals entangle with one another to form a well-uniform structure, which significantly enhances the active material's response by providing multiple channels and surface area for the electrolyte to penetrate deeper into the electrode material.¹⁶

Fig. 2 Different magnifications of the FESEM images of the (a) NMS, (b) TCX MXene, (c and d) NMS/TCX, and (e) XRD analysis of the NMS and NMS/TCX composites.

For structural features, XRD was used to identify the desired material obtained from prepared samples (Fig. 2(e)). Some major peaks reflected in the black spectrum belong to the R3̄, rhombohedral crystal (No. 148) Ni_2.5Mo₆S_6.7 phase (JCPDS: 39-0481). These peaks were confirmed with the major peaks that arise at 13.8°, 20.42°, 26.10°, 32.28°, 37.87°, and 53.5°, which correspond to the (111), (012), (003), (113), (042), and (006) planes, respectively, and are all related to Ni_2.5Mo₆S_6.7. The Ni_2.5Mo₆S_6.7 phase is formed by a sulfidation process, which replaces oxygen atoms with sulfur atoms. The hybrid Ni_2.5Mo₆S_6.7 structure has been successfully synthesized.^30,31 The diffraction peaks of the Ni_2.5Mo₆S_6.7 hybrid material, which correspond to the products of Ti₃C₂T_x MXene and Ni_2.5Mo₆S_6.7, are visible in the blue spectrum of Fig. 2(e). The peaks marked by “#” are assigned to Ti₃C₂T_x. The reflections at 2θ values of 8.7°, 17.93°, 27.35°, 36.1°, and 59.9° in the NMS/TCX hybrid indicate the presence of etched MXene. The (002) peak broadens as expected, reflecting lower crystallinity and increased disorder, which is consistent with fully etching a MXene. The decrease in peak intensity confirms the interruption of NMS sheets grown and covering the MXene sheets.^16,17 These findings confirm the presence of Ni_2.5Mo₆S_6.7 in the Ni_2.5Mo₆S_6.7/Ti₃C₂T_x MXene material and show the purity of the as-prepared composite.

The intrinsic morphological properties of the NMS/TCX hybrid nanostructure were investigated using TEM and EDS, as illustrated in Fig. 3. Ni_2.5Mo₆S_6.7 nanosheets feature an expansive, homogeneous sheet shape, indicating ultrathin crystal arrangements that are without any defects. The morphological and crystalline alignment of the NMS/TCX materials was validated by both low and high-magnification TEM analysis. Fig. 3(a) shows a TEM representation of NMS/TCX, whereas Fig. 3(b and c) shows an HRTEM image of NMS/TCX (inset: hierarchical Ni–Mo–S crystal configurations in Ni_2.5Mo₆S_6.7 nanosheets), with the flakes on Ni_2.5Mo₆S_6.7 covered over the Ti₃C₂T_x MXene sheet. From the SAED pattern shown in Fig. 3(d), the lattice spacing of 0.6508 nm validates the (101) planes of Ni_2.5Mo₆S_6.7. The SAED pattern is polycrystalline in nature, with the yellow outline indicating Ni_2.5Mo₆S_6.7 and the red outline indicating the (600) plane of Ti₃C₂T_x MXene.^16,28 The EDS mapping study (Fig. 3(e)) confirms the uniform arrangement of components such as Ni, Mo, and S, showing that sulphuration occurs during the hydrothermal process.^27,28 STEM-EDS mapping shows a uniform distribution of constituents Mo (blue), Ti (red), C (green), S (yellow), and Ni (purple) in the hybrid structures (Fig. 3(f)). The Ti₃C₂T_x MXene sheet structures act as the foundation for the ordered NMS/TCX hybrid assembly. Fig. S1(c) shows the dispersal of elements using TEM EDAX mapping. The Ti₃C₂T_x MXene layer's ultra-high surface area lowers Ni_2.5Mo₆S_6.7 nanosheet stacking during the in situ growth method, resulting in improved electron transport kinetics due to its high electrical conductivity.^30,31 The one-step in situ hydrothermal synthesis method improves the electrocatalytic capacity and stability in hybrid matrices by sulfurizing without adding contaminants during electrochemical experiments. After sulfidation, the surface roughness of the material rises noticeably. This is advantageous for increasing surface area and quickening the electrochemical reaction process.

Fig. 3 (a) TEM micrograph of NMS/TCX; (b and c) HR-TEM image of NMS/TCX, inset shows the lattice fringes and line intensity profile for the selected line; (d) SAED pattern; and (e and f) HAADF-STEM with EDS mapping analysis.

X-ray photoelectron spectroscopy (XPS) was applied to analyze the chemical composition and surface properties of the material. The complete spectra (Fig. S1(b)) indicate that the samples include Ti, C, Ni, Mo, O, and S elements. Fig. 4(a) shows that Ni²⁺, Ni³⁺, and two satellite peaks can be assigned to Ni 2p spectra. Ni 2p_3/2 contains two peaks at 855.9 eV and 858.1 eV, whereas Ni 2p_1/2 contains two peaks at 874.9 eV and 879.4 eV, showing the presence of both divalent and trivalent nickel ions.³² The addition of S results in a 0.3 eV shift in Ni 2p peaks from lower to higher energy levels, indicating that the sulfidation process facilitates the movement of Ni ions from Ni²⁺ to Ni³⁺. Fig. 4(b) depicts the Mo 3d spectra. Since all of the hybrid-structured sulfide's peaks are moved to lower energy levels, it is evident that the electrons undergo a sulfidation process to form Ni_2.5Mo₆S_6.7. The presence of the Mo element in the hybrid structure and the involvement of the element is shown by the peaks at 229.4 eV, 232.6 eV for Mo 3d_5/2 and 232.70 eV, 235.9 eV, Mo 3d_3/2, which belong to Mo⁴⁺ and Mo⁺⁶, respectively, and a small, indistinct peak at 226.4 eV originates from S 2s.^33,34 Peaks at 231.11 and 238.80 eV can be assigned to Mo–S and Mo–O bonding, respectively. As seen in Fig. 4(c), the S 2p spectra similarly revealed four distinct binding energies, with the peaks at 163.8 and 161.8 eV conforming to S 2p_1/2 and S 2p_3/2, respectively.¹⁶ Furthermore, the strong combination of Ni–S and Mo–S was responsible for the peaks at 168.6 and 169.5 eV, indicating the successful synthesis of Ni–Mo–S. Ti 2p was separated into two distinct peaks. The binding energies of 458.4 and 464.2 eV correspond to Ti 2p_3/2 and Ti 2p_1/2, respectively. This is due to the inclusion of Ti–C and Ti-X (dissolved) in the composite electrode material. From Fig. 4(d), Ti 2p was separated into two separate peaks. The binding energies of 458.9 and 464.9 eV correspond to Ti 2p_3/2 and Ti 2p_1/2, respectively. This is due to the inclusion of Ti–C and Ti-X (various functionalities) in the hybrid electrode material. The Ti 2p spectra exhibit five distinct peaks at 458.9 eV and 462.4 eV for Ti–C-T_x and Ti–O–S bonding, respectively, and at 458.6 eV and 459.59 eV for Ti(II)–O and Ti(III)–O states, respectively. Peaks arising at 283.85, 287.9, and 285 eV correspond to C–Ti, O–C, and C–C bonds, respectively (Fig. 4(e)).^16,33,34 Two peaks in the O 1s spectrum, located at 530.98 and 531.41 eV in Fig. 4(f), indicate lattice oxygen, which includes adsorbed water molecules, M–O bonding, and OH-ions.³² All things considered, XPS verified that the NMS/TCX electrode material contained an excellent elemental valence composition. The N₂ adsorption–desorption isotherm curves, showing surface area and pore size distribution, reveal type IV isotherms in Fig. S2, indicating the mesoporous nature of the materials. NMS and NMS/TCX have BET specific surface areas of 37.19 and 20.59 m² g⁻¹, respectively. The hierarchical structure resulting from the combination of MXene and Ni–Mo–S nanosheets is responsible for the composite's large specific surface area. Based on the BJH pore size analysis, the composites' pores are mostly mesopores, with pore volumes of 0.0591 and 0.077 cm³ g⁻¹ for NMS and NMS/TCX, respectively. The NMS/TCX hybrid's mesoporous structure and larger BET specific surface area may facilitate electrolyte diffusion and adsorption, thereby enhancing the charge storage capacity.

Fig. 4 High-resolution XPS spectra of NMS/TCX: (a) Ni 2p; (b) Mo 3d; (c) S 2p; (d) Ti 2p; (e) C 1s and (f) O 1s.

3.3 Electrochemical analysis

To assess the electrochemical characteristics of each active electrode, a three-electrode configuration was used on the Ni-foam substrate. Ag/AgCl was utilized as a reference electrode, Pt foil was used as the counter electrode, and the working electrode was used directly. The electrochemical performance of pristine NMS and NMS/TCX was compared in 0.5 M K₂SO₄, with the CV curves being obtained at 40 mV s⁻¹, as shown in Fig. 5(a). The three-electrode configuration of CV, GCD, and EIS was employed to conduct the electrochemical analysis of NMS and the NMS/TCX nanocomposites. The redox reaction on the CV curves of pure NMS and the NMS/TCX composite show two different peaks, indicating the pseudocapacitive nature of the NMS nanosheets and the capacitive nature of the MXene sheets. The ranges of 0 to −1 V and −0.25 to −1 V have been identified as the operational potential windows for NMS/TCX and pristine NMS, respectively. As shown by the curve, since the NMS/TCX composite electrode has a larger current response and a more significant region than the other electrodes, it guarantees a greater specific capacitance and a wider potential window. The pseudocapacitive contribution of the active materials, which inherently causes non-linear potential–time behavior during charge/discharge, is the main cause of the small asymmetry shown in the GCD profiles. Materials with redox-active sites undergo faradaic reactions, which result in tiny plateaus or curvature in the GCD profile, in contrast to only electric double-layer capacitors that display completely triangular GCD curves. Rather than any instability or adverse response, this behavior is characteristic of transition metal-based or hybrid electrodes and represents the extra charge storage mechanisms. NMS/TCX nanocomposites have a greater CV area than pure NMS because of their massive surface area and the cooperative relationship between NMS and Ti₃C₂T_x MXene.

Fig. 5 (a) Comparative electrochemical performance of the pristine NMS and NMS/TCX electrode in 0.5 M K₂SO₄. (b) The CV curves of the NMS/TCX electrode at various scan rates; (c) GCD profiles of the NMS/TCX electrode at various A g⁻¹ values; (d) the plot of the specific capacitance vs. current density (inset shows the plot of the specific capacitance vs. scan rate); (e) Nyquist plot (inset shows the simulated circuit); (f) graph of the log of the scan rate vs. current; (g) capacitive and diffusive contribution ratio at various scan rates; (h) capacitive contribution at 40 mV s⁻¹ and (i) charge storage mechanism illustration.

The recorded CV curves approximated quasi-rectangular shapes, as seen in Fig. 5(b). The CV curves stayed constant when the sweep rate rose from 5 to 100 mV s⁻¹, demonstrating that the NMS/TCX composite electrode had an impact on the dynamics of fast charge transfer.²⁸ Even at greater scan rates, the traces of all electrode CV curves are identical and show no discernible differences. The faradaic and capacitive contributions may be determined using the specific capacitance derived from CV curves. The kinetic reversibility of the faradaic processes carried out by ohmic/internal resistance and polarization is explained by the modest shift in the anodic and cathodic peaks towards positive and negative potentials with a higher scan rate. The redox peaks of the curve illustrate the pseudocapacitance properties. The redox peaks change in response to the diffusion reaction, and the forms of the CV curves increase as the scanning speeds increase.^17,28 The NMS/TCX electrode's GCD curves at various current densities are shown in Fig. 5(c). The faradaic behavior that is consistent with the CV curve results is demonstrated by the voltage plateaus in the GCD curves. The exceptional electrochemical reversibility of the electrodes is demonstrated by the GCD curves, which maintain good symmetry even as the current densities increase. At current densities of 5, 6, 7, and 8 A g⁻¹, the specific capacitances of the NMS/TCX electrode are 740.75, 666.68, 564.52, and 398 F g⁻¹, respectively, as shown in Fig. 5(d). The CV and GCD profiles of the pure NMS electrode are displayed in Fig. S4a and b. The specific capacitance was calculated to be 495.12, 260.12, and 186.30 F g⁻¹ at 3.5, 4, and 5 A g⁻¹ of current densities, respectively.

EIS was utilized to determine the conductivity information of the electrode material. A traced semicircle is shown at the high-frequency region and an inclined straight path in the low-frequency part of the Nyquist plots, as revealed in Fig. 5(e); the charge transfer resistance (R_ct) is signified by the semicircle's diameter. At a high frequency area, the diameter of the semicircle traced is also determined by the electrode material's ionic mobility, and the electron transport inset shows the circuit used for fitting. With a smaller semicircular diameter, the NMS/TCX may have a reduced charge transfer resistance, enhancing electron transit between the NMS layers and lowering the barrier to charge transfer.^16,28 The highly conductive Ti₃C₂T_x MXene sheets and NMS nanosheets connecting network performance during the composite production offer rapid and conducting pathways for charge transfer. There is less ionic resistance for the NMS/TCX hybrid electrode, as seen by the same reduction in resistance inside the material and interface. The series resistance, represented by R_s, is shown by the intersection with the X-axis and is made up of the electrolytic resistance, the inherent impedance of the electrode material, and other components. The resistance to ion diffusion at the electrolyte–electrode interface is shown by the low-frequency region's linear slope. The R_ct value for NMS/TCX is much lower at 1.99 Ω. This suggests that adding Ti₃C₂T_x MXene effectively lowers the resistance inside the material and interface.

Additionally, the CV curve at various sweep rates was used to investigate the kinetics of the NMS/TCX electrode using the power law formula, given by eqn (4) and (5),¹⁶

i_p = av^b (4)

i_p = i_s + i_d = av^b (5)

where a and b are the variables. Reflecting the charge storage mechanism, b is the slope of the plot of log(n) vs. log(i). Diffusion and surface capacitance-controlled processes are specifically represented by b values of 0.5 and 1, respectively. b = 0.5 denotes a diffusion-limited mechanism, while b = 1 denotes surface-controlled (capacitive) charge storage kinetics. This can be seen in Fig. 5(f), suggesting that a significant portion of the process is controlled by both capacitive and diffusion-controlled charge storage in NMS/TCX. Given that the generated NMS/TCX electrode reveals pseudo-capacitance behavior in both the CV and GCD curves, the b value will be in the range of 0.5 and 1. The resulting b values of 0.62 and 0.68 from the form-fitting linear graphs, respectively, imply the coexistence surface and the diffusion-controlled mechanism of charge storage. The diffusive and capacitive contributions may therefore be expressed as a proportion of the total contribution using eqn (6) and (7),¹⁶

i(V) = K₁ν + K₂ν^1/2 (6)

i(V)/ν^1/2 = K₁ν^1/2 + K₂ (7)

where K₁ and K₂ represent processes that are regulated by capacitance and diffusion, respectively. Fig. 5(h) depicts the capacitive and diffusive contributions at a sweep rate of 40 mV s⁻¹ of the NMS/TCX electrode. It reveals a 74% capacitive contribution and a 26% diffusive-controlled contribution. As seen in Fig. 5(g), the capacitive component accounts for the bulk of the charge storage with rising scan rates in relation to the charge storage approach. This is because the ion-diffusion route is limited at higher scan rates. At a low scan rate of 5 mV s⁻¹, the capacitive contribution accounts for 55% of the NMS/TCX's total charge storage. At increasing scan rates, the electrolyte ions have less time. Hence, the scan rate rises (from 5 to 100 mV s⁻¹). Both diffusive and capacitive contributions govern the NMS/TCX electrode charge storage mechanism. Fig. 5(g) illustrates that with increasing scan rates with respect to the charge storage mechanism, the capacitive component donates a larger share of the charge storage. The reason for this is that at greater scan rates, the ion diffusion pathway becomes constricted. A diffusion-dominated ion intercalation mechanism that contributes to the diffusion contribution of the NMS/TCX composite structure is produced when the NMS structure on the Ti₃C₂T_x MXene nanosheets shortens the ion diffusion distance. Furthermore, Ti₃C₂T_x MXene nanosheets offer a wide surface area and reveal electrolytic ion channels, which speed up ion transport in the electrolyte and are attributed to the significant capacitive contribution, as seen in Fig. 5(i). The NMS/TCX electrode takes advantage of the NMS/TCX hybrid system, which influences the supercapacitor electrode achieved by synergistic effects, such as Ti₃C₂T_x MXene's enhanced active sites, which improve the electrical conductivity, ion transport channels, and interfacial reactivity.^16,25

3.4 Electrochemical performance of the flexible all-solid-state LSG-NMS/TCX symmetric microsupercapacitor device

Fig. 6 displays the stepwise laser-engraved patterns in air that were used to generate graphene on a polyimide (PI) substrate. The resultant laser-scribed graphene (LSG) exhibits potential applications in miniaturized energy storage strategies.^35–37 Here, we construct all-solid-state, flexible symmetric LSG-NMS/TCX MSC devices with significantly enhanced electrochemical performance by combining the laser induction technique with the following electrodeposition of pseudocapacitive materials. The PI is then converted using a CO₂ laser to create porous LSG with an interdigitated architecture, which serves as a flexible and conductive framework for the electrode positioning of pseudocapacitive materials, in addition to acting as EDLC electrodes. To illustrate the functionality of the LSG-NMS/TCX MSC, we fabricated an MSC using an LSG electrode that was laser-scribed into polyimide tape (Kapton tape), as detailed in Section 2.6 and Fig. 6(a). In a PVA/K₂SO₄ gel electrolyte, this symmetrical in-plane interdigitated MSC was constructed and evaluated. The as-prepared LSG micro-supercapacitors (LSG-MSC) are shown in Fig. 6(b). The microdevice exhibits an active area of around 0.41 cm² and was built using 14 interdigitated electrodes, 7 of which were positive and 7 of which were negative. A digital photograph of the device is shown in the inset of Fig. 6(b), along with the dimensions for comparison with the normal scale. An FESEM micrograph displayed in Fig. S3c and d with an average spacing of about 350 µm demonstrates the distinct MSC pattern, along with a highly porous framework of vertically aligned graphene sheets. Fig. 6(c) shows the decoration of the NMS/TCX hybrid material over the LSG electrodes, which were assembled using the spray coating method for an equal mass balance between the electrode materials. A cross-sectional micrograph is shown in Fig. S1(a), which shows that an overall thickness of 56.3 µm of the LSG-NMS/TCX electrode was adhered on the PI flexible support. The mechanism involving the process of laser-scribed graphene (LSG) interacting with a polyimide (PI) substrate is a direct photothermal conversion, in which a porous, graphitized carbon network stays intact after the targeted high-energy laser breaks down PI, releasing different gases (CO, CO₂, and N₂). Since the intense photothermal ablation of PI and the following carbonization/graphitization of its chemical backbone allow for the in situ production of LSG patterns that are securely fixed to the substrate, these processes primarily control the interaction.^38–40 The formation of a highly porous graphene vertical framework was confirmed with XRD and Raman spectroscopy. An evident peak at a 2θ value of around 25.7° in the LSG XRD pattern (Fig. S3a) is attributed to the crystal phase (002) plane, with a matching interlayer spacing of 0.34 nm. Graphitized LSG was produced when the CO₂ laser beam caused an extremely high localized temperature (>2500 °C). LSG was further investigated using Raman spectroscopy (Fig. S3b). Three distinctive bands, representing classic D, G, and 2D bands, were seen in the Raman spectra of LSG at 1351 cm⁻¹, 1582 cm⁻¹, and 2690 cm⁻¹, respectively. The distinctive peak located at 1351 cm⁻¹ is associated with the D band of the oxygen functional groups that remain. Sp² hybridized C–C bonds of LSG are confirmed by a strong G band at 1582 cm⁻¹. The location of LSG's 2D band is 2690 cm⁻¹. The strong G and 2D bands seen in LSG confirmed graphene's exceptional crystallinity.^9,37 Its high conductivity and exceptional flexibility make it worthwhile to use as a current collector for the MSC.

Fig. 6 (a) Schematic of the stepwise fabrication process of the NMS/TCX microsupercapacitor; (b) FESEM image of the interdigitated LSG-NMS/TCX MSC device showing fingers and spacing. The inset shows a digital photograph of LSG-NMS/TCX MSC; (c) high-magnification image shows the distribution of the NMS/TCX material of the LSG electrode; and (d) schematic of the working mechanism of the charge storage and intercalation of ions in the energy storage performance for the NMS/TCX composite on the LSG electrode.

Because of the strong mechanical adherence, electrical conductivity, and flexibility offered by this precise connection, LSG-on-PI is an ideal option for adaptable and flexible supercapacitors. Electrostatic attraction, π–π stacking, hydrogen bonding, or covalent fixing with residual oxygen/nitrogen functions on LSG are the principal channels of interaction when LSG is decorated with active materials. Due to these interactions, the hybrid electrode is more effective for supercapacitor applications by improving the mechanical stability, ion diffusion, and charge transfer.^35–37 Here, the MXene functional groups are actively bonding with LSG, thus forming a firm interaction between the substrate and active electrode materials.

The outstanding charge storage capabilities of the LSG-NMS/TCX MSC device are demonstrated by the CV curves at all scan rates, which display a pseudocapacitive and well-maintained form in the range of 0 to 1.6 V (Fig. 7(a)). As illustrated in Fig. 6(d), the highly porous architecture and sheet-like morphology of LSG-NMS/TCX MSC provide short ion–diffusion pathways for quick electrolyte adsorption and desorption as well as an in-plane interdigital configuration that permits free movement of electrolyte ions, resulting in the superior rate-capability of the LSG-NMS/TCX MSC. The CV curves of LSG-NMS/TCX MSC at various scan rates, spanning from 5 mV s⁻¹ to 200 mV s⁻¹ and at a potential window of 1.6 V, are shown in Fig. 7(a). As the scan rate increases up to 100 mV s⁻¹, the CV curves retain their irregular rectangular shape without any distortion, demonstrating LSG-NMS/TCX MSC's excellent reversibility and quick charge/discharge capacity. To further evaluate the device's electrochemical performance, galvanostatic charge–discharge (GCD) experiments were carried out, as shown in Fig. 7(b). The LSG-NMS/TCX MSC performs exceptionally well, as seen by the result, which shows consistent linear potential–time curves across various current densities. The plot of the areal specific capacitance vs. current density of the LSG-NMS/TCX MSC is shown in Fig. 7(d). The excellent areal capacitance was calculated to be 208.33 mF cm⁻² at a current density of 5 mA cm⁻². At current densities of 5, 6, 7, 8, 9, and 10 A cm⁻², the CN-LSG MSC's volumetric capacitance was determined to be 208.33, 181.82, 167.46, 154.89, 141.72, and 140.03 mF cm⁻², respectively. Remarkably, even at an extraordinarily high current density of 15 mA cm⁻², the accelerated charge transfer kinetics are made feasible by the nanosheet-like structure over a porous graphene network, and better conductivity offered by the LSG support accounts for the LSG-NMS/TCX MSC's exceptional performance.^17,25,39 This is further corroborated by the Nyquist plot and the low charge transfer resistance (R_ct) of 168.4 Ω (Fig. 7(c)). Furthermore, the outstanding long-term cyclic stability was demonstrated by the LSG-NMS/TCX MSC and its outstanding capacitive performance. The device maintains 94% of its capacitance value over 10 000 charge–discharge cycles at a high current density of 15 mA cm⁻², demonstrating the device's strong rate performance, as displayed by Fig. 7(e). Considering the long-term stability, the coulombic efficiency exceeded 99%, indicating reliable LSG-NMS/TCX MSC operations. Notably, during almost 10 000 cycles, the GCD curve's overall shape was constant, as shown in the inset of Fig. 7(e). Furthermore, the comparison and practical implications, and the performance metrics of the LSG-based MSC devices using various active materials are provided in Table 1. Fig. 7(f) displays the Ragone plot of the LSG-NMS/TCX MSC, which, according to Table 1, has an energy density of around 65.10 µWh cm⁻² at a power density of 4212.1 µW cm⁻² compared to other LSG-based microsupercapacitor devices fabricated using various composite materials.^{12–15,41–47} Remarkably, its energy density surpasses that of several LSG-based MSCs (Table 1).

Fig. 7 Electrochemical evaluation of the LSG-NMS/TCX MSC; (a) CV curves at scan rates between 5 and 100 mV s⁻¹; (b) GCD curves at various current densities (between 5 and 10 mA cm⁻²); (c) Nyquist plot, inset shows the simulated circuit; (d) the graph of specific capacitance at various current densities and scan rates; (e), long-term cyclic stability of the LSG-NMS/TCX MSC, inset shows the first 100th, 5,000th and 10,000th GCD cycles at 15 mA cm⁻² of current density; and (f) Ragone plot of the LSG-based MSC.

Table 1 The comparison of the electrochemical performance of various LSG-based MSC devices

Material	Areal capacitance (mF cm^−2)	Energy density (µWh cm^−2)	Power density (µW cm^−2)	Cycling stability%/cycles	Ref.
L-LSG/Mn3O4	136.19	10.6	266	93.4/5000	12
LIG/NiCo2S4	30.4	16.9	367.5	122/5000	41
MXene/LSG	2.58	93.5	13	97.7/10 000	42
MoS2/MnS/GR	58.3	7	49.9	93.6/10 000	14
3 wt% CB-am PES	47.3	9.46	300	97/5000	43
LIG-FeOOH//LIG MnO2	21.9	9.9	11 853.3	84/2000	44
LIG-PANI-15	361	8	1100	97/6000	44
LIG-MnO2-2.5	281	21.7	2248	82/6000	44
OPL-LIG-7030	30.77	1.76	250	88.4/5000	45
S-LrGO/S–MnO–Mn3O4	73.25	14.65	1290	90/5000	13
LIG/MoS2	14	2.8	1000	100/2000	46
LIG-Ni-CAT MOF	15.2	4.1	7000	87/5000	47
LSG-B 1T-MOS2/MXene	72.31	5.7	77.1	100/10 000	15
LSG-NMS/TCX	208.33	65.10	4212	94/1000	Present work

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Additionally, the constructed LSG-NMS/TCX MSC device demonstrated exceptional mechanical flexibility. For instance, the device was subjected to various bending and twisting deformations. As seen in Fig. 8(a), the device was twisted in a different direction. Fig. 8(b) shows the LSG-NMS/TCX MSC's well-maintained CV curves at bending angles of 0°, 60°, 90°, and 120°. Regardless of the bending deformation, the LSG-NMS/TCX MSC's initial capacitance is the least impacted (Fig. 8(c)), demonstrating the device's mechanical durability and strong adhesion of NMS/TCX materials to the micropatterned LSG. The exceptional performance of the LSG-NMS/TCX MSC can be attributed to the combined impacts of the NMS/TCX ordered architecture, ultrathin thickness of the NMS nanosheets, and the in-plane arrangement on a porous graphene framework providing an extensive surface area and active sites to interact with the electrolytic ions and a highly conducting current collector. The scalable integration capabilities of the LSG-NMS/TCX MSC devices are methodically examined in both series and parallel configurations since the real applications require great energy and power density. As illustrated in Fig. 8(d) and (e), which shows CV and GCD profiles when three devices are arranged in parallel, the output current changes and discharge time are seen to be three times greater than when one MSC device is used alone. This demonstrates the MSC device's high scalability for application in real-world circumstances. The ultrathin NMS nanosheets give a quick ion transport channel and wide ionic accumulation, which explains the remarkable performance of solid-state flexible MSCs. The MSC is given more flexibility by the NMS/TCX and LSG's 2D architecture. The in-plane configuration facilitates electron transport by shortening the diffusion pathway. Furthermore, the tensile stress–strain test of LSG was performed to examine the mechanical durability features. Significantly, the LSG electrode exhibited a high tensile strength of 13.403 MPa. This indicates that it is not significantly altered compared to the non-scribed pure PI substrate with 13.148 MPa. The break load of LSG shows a better load capacity of 6.920 kg compared to the PI substrate, which is 6.640 kg. The stress–strain features and flexibility studies show the strong mechanical possessions of the LSG electrode. The results of the tensile test parameters for the LSG electrodes are shown in Table S1. Fig. 8(f) also provides the post-operation analysis of the LSG-NMS/TCX MSC that shows the substantial adhesion and well-maintained stability are provided for the device by the interaction of the NMS/TCX with LSG (inset, Fig. 8(f)). This streamlined and quick way of developing flexible and solid-state MSCs may effectively achieve large-scale production, while significantly avoiding costly and complicated fabrication techniques, including multiple-step lithographic fabrication, photoresist consumption, and plasma etching of the material. Also, exploring different electrolyte systems, including ionic gels, hydrogels based on neutral salts, or solid-state polymer electrolytes, may improve the device's voltage window, ionic mobility, interfacial stability, and long-term durability. Most significantly, the LSG-NMS/TCX MSC conductive, additive-free, and binder-free production technique efficiently increases volumetric performance without compromising its mechanical flexibility. Consequently, we provide a substantial addition to the area by presenting a practical and affordable approach for producing MSC. In contrast to more traditional methods that could need intricate or costly production processes, our approach is straightforward and cost-effective without compromising efficiency. The capacity of our method to reduce any oxidation during laser writing procedures is one of its special benefits. Maintaining the integrity and functionality of materials is a critical problem, and our approach successfully overcomes it to guarantee the longevity and effectiveness of MSC.

Fig. 8 Investigation of the scalability and flexibility of the LSG-NMS/TCX MSC electrodes. (a) CV curves at 40 mV s⁻¹. Inset shows the digital images of the fabricated LSG-NMS/TCX MSC device under changed twisting deformations; (b) CV curves at various bending angles between 0 and 120° at a scan rate of 40 mV s⁻¹; (c) areal capacitance of the LSG-NMS/TCX MSC obtained at various operational conditions (varied bending angles and twisting deformations); (d) CV curves (at 100 mV s⁻¹) of one MSC and three MSCs coupled in series and parallel. A digital image is included in the inset and (e) GCD curves recorded of one MSC and three MSCs coupled in parallel and series configurations; and (f) cross-sectional FESEM image of the LSG-NMS/TCX MSC device after all electrochemical testing; inset shows the higher magnification image.

4 Conclusion

In summary, we designed an efficient and adaptable method for fabricating miniature and wide-area Ni–Mo–S/Ti₃C₂T_x MXene on LSG to construct a solid-state micro-supercapacitor. With the addition of Ti₃C₂T_x MXene, the Ni–Mo–S/Ti₃C₂T_x MXene hybrid's capacitance is measured to be around 740.75 F g⁻¹ at 5 A g⁻¹. Owing to the substantial capacitive contribution, Ti₃C₂T_x MXene sheets have a large surface area and exhibit electrolytic ion channels, which accelerate ion transport in the electrolyte. The device exhibits an excellent areal capacitance of 208 mF cm⁻² at a current density of 5 mA cm⁻². Additionally, even after 10 000 charge–discharge cycles, the LSG-NMS/TCX MSC device maintained an extraordinarily high rate capability of 94.6%, delivering an extraordinary energy density of 65.10 µWh cm⁻² at a power density of 4212 µW cm⁻². The mechanical flexibility of the constructed LSG-NMS/TCX MSC is unaffected by a range of twisting and bending angles. The LSG-NMS/TCX MSC demonstrated exceptional mechanical flexibility when subjected to bending deformations. Additionally, by employing the series and parallel configurations of MSCs, which increased the capacitance value and operating voltage, the LSG-NMS/TCX MSC device's scalability to meet real-world applications was examined. In practical terms, this innovative approach can provide new opportunities for the straightforward and logical fabrication of advanced, high-performance flexible electronics using a number of hybrid nanostructures based on transition metals. The results highlight the possibility of Ni–Mo–S/Ti₃C₂T_x MXene hybrid nanosheets for high-performance microscale energy storage, and provide additional perspectives on the development of flexible and compact energy storage devices of the future.

Conflicts of interest

The authors declare no conflicts of interest.

Data availability

The corresponding author can provide the data supporting the study's conclusions upon reasonable request.

Supplementary information (SI) is available. See DOI: https://doi.org/10.1039/d5ta07853a.

Acknowledgements

The authors extend their appreciation for the financial assistance provided by the ANRF Core Research Grant (grant no. CRG/2022/000897) and Jain University Grant (JU/MRP/CNMS/118/2025). C. S. R. acknowledges support from the National Research Foundation of Korea under the Brain Pool program, funded by the Ministry of Science and ICT, South Korea (grant no. 2023-00217581). The work is further supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (grant no. RS-2024-00217581 and 2024-00345983).

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